Toothbrushes are known which include a wear indicating portion that changes color when the toothbrush is at or near the end of its useful life. One version of a wear indicating toothbrush includes toothbrush filaments (bristles) having a colorant and being adapted to provide a color intensity which can change in response to increased use of the bristle to provide a signal indicative of bristle wear. A line of toothbrushes having such a bristle has been successfully marketed by Oral-B Laboratories, Belmont, CA, under the Indicatoro brand.

U. S. Patent No. 5,340,581 to Tseng et al. discloses a wear-indicator oral brush that includes a matrix containing a colorant (e. g., a dye) and a water- leachable substance that is released from the matrix when the oral brush is used to cause the matrix to change color after repeated (at least 5) typical uses.

Toothbrushes in which a part of the brush changes color to indicate wear take a relatively long period of time to change color. In the brush of the previous paragraph, if a person was brushing three times a day, it would take two days of brushing to effect a visible color change. If the person were brushing twice a day it would take three days of brushing to effect a visible color change. Such a relatively long period of time for the color to change can be a problem where the color change is intended to accomplish something other than to indicate wear. For example, in a children's toothbrush, it would be desirable to effect a color change to the brush relatively more quickly than disclosed in the prior art in order to enhance the entertainment value of the brush. Likewise, a faster color change would be preferable to indicate the winner of a contest in which one toothbrush would change color to indicate the winner of the contest.

A toothbrush made by Jordan and distributed by DEP Professional Oral Care includes a thermochromic material in the handle of the toothbrush. At room temperature and below the handle is green in color. When the handle is exposed to hot water or a human hand, thus elevating the temperature of the handle above room temperature, the handle turns from green to an off-white/yellow color.

When the temperature of the handle cools down again, it reverts to its original green color.

The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a toothbrush includes a handle, a head extending from the handle, and a multiplicity of bristles extending from the head. At least a portion of the toothbrush is a first color prior to the portion being exposed to liquid for the first time. The portion changes to a second color after the portion has been exposed to liquid for a period of time which is less than the accumulated time which passes during five typical uses of the toothbrush to brush a person's teeth. The change in color is caused by removal from the toothbrush of at least part of the portion by the liquid. The change in color is perceivable by the unaided human eye.

By providing a color change to at least part of a toothbrush faster than has been disclosed in the prior art, the entertainment value of the toothbrush is enhanced. In children's toothbrushes, the relatively more rapid color change will increase the pleasure children obtain from their toothbrush. Also, in a contest where one toothbrush of a certain model changes color to indicate a winner of the contest, relatively rapid color change is desirable so that a person can quickly learn whether or not they have won the contest.

These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.

FIG. 1 is a top view of a toothbrush; FIG. 2 is a perspective exploded view of a logo on the toothbrush in FIG. 1; FIG. 3 is a top view of another toothbrush; and FIG. 4 is a top view of the toothbrush of FIG. 3 after the toothbrush has changed colors.

Beginning with Figure 1, a toothbrush 10 includes a handle 12 and a head 14 extending from the handle. A multiplicity of tufts of bristles 16 are secured to the head with metal fasteners (not shown). Alternatively to using

fasteners to secure the tufts to head 14, the tufts can be hot tufted (insert molded) into head 14. The tufts extend away from head 14 in a direction perpendicular to the top surface of the head. A logo 18 is affixed to handle 12 at an end of the handle opposite head 14. A series of thumb grips 20 are provided on handle 12.

Toothbrush 10 is made by the following process. Unitary handle 12 and head 14 are formed of a plastic, such as polypropylene or a polyurethane (e. g.

Isoplast), in an injection molding machine. In this embodiment, the plastic handle/head is made of a transparent blue plastic. The handle/head may optionally then be moved to an additional injection molding machine for application of rubber (e. g. Kraton) to portions of the handle. For example, thumb grips 20 can be made of rubber.

After the handle/head is injection molded, logo 18 is applied to handle 12 by a hot-stamp process. In this process, a solvent based dry ink on a donor tape is positioned against the handle with the ink facing the handle. A die in the shape of the logo and held at a temperature of about 500 degrees Fahrenheit is pressed onto the tape and thus onto the handle at about 90 psi to brand the ink onto the handle in the shape of logo 18. The die is held against the tape for about 0.5 seconds, thereby transferring the ink, but not the tape, to handle 18. The die also softens the plastic on the handle, causing logo 18 to also be physically pressed into the handle slightly. In other words, logo 18 is slightly concave into handle 12. The ink is water-proof and will adhere to handle 12 even after exposure to water for extended periods of time.

Finally, the handle/head is transferred to a tufting machine where tufts of bristles 16 are secured to head 14. In this process, well known to those skilled in the art, a metal fastener (staple) is derived against the middle of a tuft of bristles to fold the tuft in half. The fastener is driven into a precored blind hole in the head, formed during injection molding, to anchor the staple and thus the tuft to head 14. Again, an alternative way to secure the tufts to the head is with a hot tufting (insert molding process).

Standard fasteners are made of an alloy of zinc, copper and nickel.

Such a fastener is corrosion resistant. It may be desirable to be able to identify a certain toothbrush from one or more other toothbrushes which appear substantially

identical to the certain toothbrush when viewed with the unaided human eye. In this event, the fasteners used in making the certain toothbrush can be made of only zinc and copper (brass). Although the zinc and copper fastener appears the same as the zinc, copper and nickel fastener to the unaided human eye, the difference between these two fasteners can be identified by scientific analysis (e. g.

SEM/EXDA OR ICP/AES). As such, the certain toothbrush can be identified from one or more other toothbrushes which appear substantially identical to the certain toothbrush when viewed with the unaided human eye.

Alternatively to making the fasteners of a different material, the fasteners of the certain toothbrush can be micro-engraved and/or etched. Further, the fasteners of the certain toothbrush can be driven into head 14 at a different angle and/orientation than the staples of the other toothbrushes.

With reference to Figure 2, logo 18 will be described in further detail. A first layer 22 of the logo is applied to handle 12 by the hot-stamp process described above. In this embodiment, layer 22 is formed of white ink. A second layer 24 is a Super Brass Spray ZY0175 paint available from ICI Paints. The second layer can also be made of Zynolyte 500 Series Gold Epoxy Paint by Zynolyte Products. This paint is gold in color and is applied over aligning a mask with a cut-out in the shape of logo 18 over layer 22. Such a mask can be made by scanning the logo into a digital format and then using a computer to drive a printer to print out the mask. The paint is then sprayed through the mask on top of layer 22. After this paint dries, it is water proof. Gold layer 24 can alternatively be applied by vacuum metalizing or sputtering.

A third layer 26 of the logo is applied over second layer 24 in the same manner described above (i. e. applying layer 26 through a mask). Third layer 26 is PRO WHITE paint available from Daler Rowney, Ltd. This paint is water based, white in color, and not a health risk if ingested in small quantities. Even after the third layer dries, it is not liquid proof. The third layer will dissolve and wash away in the presence of liquid (e. g. water and/or human saliva). Various tests (e. g. ultra-violet light exposure, thermal variations, simulated shipment, shaking and humidity) were conducted on logo 18 and verified that layer 26 would remain intact prior to being exposed to liquid. Middle gold layer 24 should be sandwiched

between white layers 22 and 26 such that layer 24 is not visible until layer 26 is washed away by liquid. As an alternative, layer 26 can be applied as a decal using an internegative transfer (INT) Decal. Accordingly, the entire logo 18 could be applied to handle 12 as a multilayer hot-stamp or using multilayer pad printing/decals.

Logo 18 can also be used to identify the certain toothbrush described above with reference to the fasteners used to secure tufts of bristles to head 14.

When the certain toothbrush is new, logo 18 appears white in color. After the logo is exposed to liquid, at least a portion of the material in white layer 26 of the logo dissolves revealing gold layer 24 which does not dissolve, thus effecting a color change to logo 18. Layer 26 preferably dissolves sufficiently to reveal the gold layer to the unaided human eye prior to the amount of time logo 18 would be exposed to liquid during five uses of the toothbrush to brush a person's teeth. This amount of time is estimated to be 15 minutes. How fast layer 26 dissolves is a function of the formulation of layer 26, including the polymer used and the polymer's molecular weight.

The use of a special fastener and logo 18 to identify a certain toothbrush can be used in the event a toothbrush distributor wants to hold a contest.

In this scenario, one certain toothbrush is provided with logo 18 and with fasteners made of only zinc and copper. All other toothbrushes have a logo which has only layer 22 and not layers 24 and 26, and have fasteners made of zinc, copper and nickel. The distributor advertises that the consumer who finds the"gold"toothbrush will win a prize (e. g. a sum of money). Consumers are told to expose the logo on the toothbrush to water and rub the logo for 10 seconds. Only the certain toothbrush with logo 18 will change from white to gold. All other toothbrushes' logos will remain white in the presence of water when rubbed because these logos only have layer 22. When a consumer presents a certain toothbrush with a gold logo, the fasteners of the presented brush are analyzed to make sure they are made of only zinc and copper. The fasteners are a double-check to make sure the consumer presenting the brush is not forging the gold logo. An additional way to further identify the certain toothbrush is to add an ingredient (e. g. barium sulfate) to the plastic from which the certain toothbrush's handle/head are made.

A three layer logo 18 is used because if a two layer logo were used (only layers 24 and 26) a consumer could view logo 18 through the translucent handle and possibly see the gold layer 24 without having to remove layer 26 with water. A two layer logo could be used if handle 12 were made of an opaque plastic. In this event, layer 24 would be applied directly to the polypropylene handle. Plastic additives can be included in the gold paint to make layer 24 more adhesive to the plastic. As such, the handle can be treated with Loctite 7701 by Loctite Corp., a polyolefin primer or Tantec EST Spot Generator to enhance adhesion of layer 24 to the handle.

Turning to Figures 3 and 4, a further embodiment of the invention will be described. Here, a toothbrush 30 is disclosed which does not have a logo.

Toothbrush 30 is made of an opaque plastic of a first color (e. g. green) in a manner similar to how brush 10 was made. The handle 32 and head 34 are covered with the PRO WHITE paint described above by spray painting the handle and head prior to securing tufts of bristles to the head. When the consumer uses the toothbrush and exposes it to liquid, the white paint will dissolve to reveal a green toothbrush.

The color change is represented by the shading change of the handle/head between Figures 3 and 4.

Such a toothbrush would be very attractive to children who would find the changing color toothbrush very interesting. Although the entire handle and head are described as being covered with the paint, only part of the handle and/or head can be covered with the paint. Additionally, some or all of the bristles 36 may be covered with the paint.